1. Field of the Invention
The invention relates to article handling systems and, more particularly, relates to a method and apparatus for palletizing and/or depalletizing layers of articles on or from stackable pallets and to a stackable pallet usable therewith.
2. Background of the Invention
Article handling systems are well known for stacking layers of articles on a pallet or for removing layers of articles from a loaded pallet. Article handling systems that stack layers of articles on a pallet to load the pallet generally are known as palletizers. Article handling systems that remove layers of articles from a pallet to unload the pallet generally are known as depalletizers. Some article handling systems are capable of operating either as a palletizer or as a depalletizer, using at least some common equipment of the system for both palletizing and depalletizing operations. A palletizer is disclosed, for example, in U.S. Pat. No. 4,708,564 to Malrea. A combined palletizer/depalletizer is disclosed in U.S. Pat. No. 5,207,727 to Pierce et al.
Palletizers, depalletizers, and combined palletizers/depalletizers typically are designed to stack and/or unstack as many as 30-40 boxes or other articles on and/or from a relatively large pallet. These systems therefore must be relatively large to accommodate fully-stacked pallets--so large in fact that they are not easily located in a storage and retrieval system central aisle for access by automated storage and retrieval machines (SRM's). Stacks of pallets instead are conveyed to and from the article handling system by dedicated conveyors--thereby further increasing the space requirements of the system.
Another problem associated with standard palletizers and/or depalletizers is that they are poorly suited for rapidly handling relatively small numbers of articles. As mentioned above, a fully-loaded pallet of the type typically used in palletizers and/or depalletizers supports 30-40 cartons or other articles or even more. Many businesses, such as the typical meat packing business, seldom ship or receive batches of more than 9-12 cartons or other articles. Palletizers and/or depalletizers used in these applications therefore must routinely handle partially-loaded pallets using an over-sized system that operates at less than 1/3 to 1/2 of its capacity at a considerable waste of space and resources.
A conventional wooden pallet used in palletizers and/or depalletizers also cannot be loaded or unloaded if it is stacked on top of other pallets. Nor can they be handled by SRMs commonly used to handle trays or pans. Typical prior art systems therefore require that pallets be delivered to and from a staging area one at a time. This requirement adds additional complexity and expense to a palletizing operation or a depalletizing operation.